1978 Kawasaki Z1R-TC: Turbo Power

The appeal of turbo power launched a brace of unlikely motorcycles, as well, including the Honda CX500/650 Turbo, the Kawasaki GPz750 Turbo, the Yamaha XJ650 Seca Turbo and Suzuki’s XN85. Almost forgotten in the rush was the first turbo bike, the 1978 Kawasaki Z1R-TC.

Notoriously reticent about horsepower figures, the Rolls-Royce company adopted a snooty retort to inquiries about the output of its automobile engines: “Sufficient,” was all they would say. But when the pavement-bending Bentley Mulsanne Turbo first rolled out of the Derby Works in 1982, the stock answer would no longer do. It became: “Sufficient — plus 50 percent.”

The 50 percent came from a Garrett AiResearch turbocharger bolted on to R-R’s 412ci V8. The prestige car maker wasn’t alone in its approach to instant horsepower, and the 1980s became the turbo decade. Saab, Volvo and others adopted turbos to pep up their 4-cylinder engines, and many American automakers used turbocharged V6s to replace gas-guzzling V8s as a way of meeting fuel consumption targets.

The appeal of turbo power launched a brace of unlikely motorcycles as well, including the Honda CX500/650 Turbo, the Kawasaki GPz750 Turbo, the Yamaha XJ650 Seca Turbo and Suzuki’s XN85. Almost forgotten in the rush was the first turbo bike, the 1978 Kawasaki Z1R-TC.

Boost

The first widespread use of turbochargers was to boost the performance of high-altitude World War II aircraft like the B-17 Flying Fortress and the P-38 Lightning and P-47 Thunderbolt fighters. In 1978, Kawasaki’s flagship 1,000cc model needed a boost. The 1970s had become a game-changing decade in motorcycle development, and Kawasaki was being left behind. In spite of leapfrogging Honda’s CB750 with the double overhead cam 903cc Z1, Kawasaki’s big bike development had stalled in mid-decade.

Though revolutionary when introduced, the Z1 wasn’t perfect. The mild steel double cradle frame flexed under load, the 36mm forks were under-specified, and the rear suspension was over-sprung and under-damped. To lighten the steering, Kawasaki’s engineers gave the Z1 a sharp, 26-degree steering rake, but it came at a price; sudden direction changes would induce weaves, which, combined with the lack of trail, could quickly get out of hand. Neither was the single disc/drum brake combo up to hauling 530 pounds of motorcycle down from 125mph.

When the Suzuki GS750 arrived in 1977, Kawasaki countered with the triple disc-brake KZ1000. It looked cooler, and maybe stopped better, but the extra 100ccs produced little if any extra power, and the flexy frame remained. The liter-class still set the performance benchmark, but with the GPz1100 a couple of years away, Kawi’s Z-bike needed a makeover to extend its life.

Enter the Z1R

The Z1R was more a styling exercise than a new motorcycle. The R-bike featured a handlebar fairing — a first on a Japanese sport bike — the squared-off lines of which were echoed in the “coffin” gas tank, triangular side panels and swooping tailpiece, all finished in ice-blue metallic paint. You certainly couldn’t miss it — which was the idea.

Underneath the bodywork the KZ1000 engine (now with 28mm versus 26mm carbs) went into the same flexy frame and exhaled through a new 4-into-1 exhaust. Claimed horsepower was up to 90 at the crank (though period dyno tests failed to find much more than the stock KZ). New cast alloy wheels were 18-inch front and rear (the KZ1000’s wire front wheel was 19-inch), and drilled triple discs handled slowing the big blue bike.

It was when reviewers actually rode the Z1R that the wheels started to come off — off the ground, anyway. Although it had extra gusseting, the R bike used essentially the same frame as the earlier, lighter Z1. The smaller front wheel reduced the marginal trail even more, making the R even livelier than its predecessor, plus it had stiffer rear springs and increased damping. “It doesn’t roll over bumps: it bounces from crest to crest,” wrote Cycle Guide in a period review. The same magazine found the handling “less than road racer precise thanks to numerous rubbery frame tubes.”

So Kawasaki had created a high-powered pogo stick with suspect handling. Probably the last thing it needed was more power, and a lot more power at that ...

Pumping iron — the Kawasaki Z1R-TC

The Z1R-TC idea was the brainchild of former Kawasaki executive Alan Masek. Masek had big plans for his newly-formed Turbo Cycle Company, and noted that slow Z1R sales meant there were surplus bikes in the supply chain. At the same time, Kawasaki needed something to wow the market while waiting for the GPz1100 to arrive.

It was the perfect opportunity for Big Green: Masek would take stock Z1Rs, fit an American Turbo Pak compressor and its ancillaries, then feed the converted bikes back into the Kawasaki dealer network. Any regulatory or liability issues could be diverted at TCC, while Kawi reaped the benefits of winning the horsepower war.

For the first batch of 250 or so Z1R Turbos, TCC simply replaced the header pipes with a new cylindrical exhaust collector (known to TC fans as “the log”) to feed the ATP turbo unit, added an adjustable wastegate, installed a new open exhaust to eliminate back-pressure in the turbo and added a boost gauge to the dashboard. Apart from TC decals on the side panels — and a notice that the Z1R-TC should only be used by experienced riders — that was pretty much it. A supplied list of do’s and don’ts also included a warning to owners not to attempt to increase boost by tampering with the wastegate setting, which was a bit like telling a dog not to chew a bone. Every TC buyer was required to sign a liability waiver, too. What could possibly go wrong?

For starters, the Z1R-TCs offered to the press for testing were specially prepared. The engines had been stripped so the built-up crankshafts could be welded to prevent twisting while the valve and clutch springs were replaced with stronger items. None of these modifications were standard on “production” bikes, though they could be special ordered at extra cost.

Neither was the engine fitted with a rev limiter, an innovation that would have to wait until electronic ignition arrived. This was a potential problem on the TC, considering a turbocharger creates what is essentially a positive feedback loop. In a normally-aspirated engine, gas-flow efficiency typically limits the revs the engine will achieve. But with the throttle wide open, a compressor-fed engine will continue to spin up until the valves float or start hitting the pistons. Catastrophic failure follows, often caused just by missing a gear. Not surprisingly, the TC was sold without a powertrain warranty, and buyers had to sign off to that effect, with a witness! Further, the TC’s performance capability far exceeded the limitations of the stock Z1-R chassis on anything but a billiard-table-smooth drag strip. And the TC listed at $1,400 more than the stock Z1R’s already hefty $3,695 sticker.

Practice

As the Z1R-TC’s turbo is set up so the boost only goes into positive territory above 4,500rpm, performance below that level should have been similar to a stock Z1R. However, period testers, including Cycle Guide’s team, found the TC to be pretty ornery to live with. It was difficult to start from cold, requiring a long warm-up, and then ran roughly unless given regular open throttle runs to “clear its throat.” It also seems the turbocharger selected for the TC was larger than ideal, meaning it was slow to respond, resulting in significant “turbo lag” before delivering its performance in a rush that required a close watch on the tachometer. Maneuvers like overtaking required careful planning, so testers would open the throttle and hold the bike back on the brakes until a passing opportunity arose.

Cycle Guide also found that their TC smoked on the overrun and needed additional oil every few hundred miles. But adding oil wasn’t easy, as the turbo’s oil return screwed into the oil filler, requiring tools to remove the return just to add oil. Worse, the Z1-R’s on-board tool kit was missing, its allocated space filled by the Bendix carb’s electric fuel pump! Other niggles included an easily defeated alarm system — and the fact that the turbo kit’s fasteners were SAE sizes while the rest of the bike was metric.

So the TC might not have been ready for prime time on the street, but it certainly performed on the strip, delivering sub-11-second quarter-miles at 125mph-plus — until the clutch expired, anyway. Cycle Guide was even more impressed with the TC’s open road performance boost: “Nothing comes close to the out-of-the-slingshot sensation you get when the boost comes up near the 10 pound maximum,” they said, noting at the same time that the TC probably approached the limit for the tire technology of the day.

TC 2

In spite of its well-publicized problems, the TC sold reasonably well and returned for 1979 with new disco-era black and orange livery from Southern California design house Molly Designs. These “new” TC turbos were still based on 1978 Z1Rs, as Kawasaki didn’t offer the model for 1979 owing to slow sales in 1978. And while the basic TC package was similar, there were many detail changes, most noticeably a new “spider” 4-into-1 collector that promised improved low-rev gas flow for better slow running, reduced turbo lag, and a smoother transition to boost mode. Other changes included a baffle in the oil pan to prevent oil starvation, the oil return moved to a new fitting where the kickstarter used to be to allow full access to the oil filler, better metering for the turbo’s oil supply, a smaller fuel pump and a new centerstand.

Also changed was the “factory” wastegate setting, now maxing out at 6psi on Cycle Guide’s tester (instead of 10 for the first version), a level at which TCC suggested the engine would provide “faithful service.” However, they still recommended that owners fit stronger valve and clutch springs and have the crankshaft welded — as well as lower the engine’s compression, retard the timing and only use 107 octane gas. Minor details.

Mark Scott owns the Molly Designs Kawasaki Z1R-TC featured here. “This is my third one,” he says, noting he sold one to a Japanese collector. “I got this one at auction in Las Vegas in 2010, so now I have two. It’s very original, low mileage, stone stock. It has a deep oil pan and the welded crank as options. The carburetion was, in my opinion, the absolute Achilles’ heel,” Mark says. “They used a Bendix that was built for Harleys. It would not carburate consistently and constantly fouled plugs — you had to keep blipping the throttle no matter what, which was nice for a while, but it got a little tiring if you were trying to ride in traffic. I still have the stock carb, but I bought a Mikuni 42mm flat slide. Now it idles, and it doesn’t load up. If it could have had a flat slide Mikuni at the time, it probably would have done a lot better.

“The turbo was a bit big — they just used what they had available — which meant quite a bit of lag, and the boost didn’t really come in until quite high up. I also have a 1984 Kawasaki 750 turbo, which is a ballistic missile — it has a much smaller turbo, much less lag, and fuel injection, which got rid of the whole carburetion problem.” What’s the Z1R-TC like to live with? “Off boost, it runs like a Z1R,” Mark says. “Below 4,000-5,000rpm it rides like a nice strong 1,000cc bike. The difference comes when you spin it up and it reaches six grand, and then it’s like whoaaaa! It just becomes a completely different kind of animal.”

The biggest problem, Mark says, is that you need a really good stretch of straight road to get it up on the pipe — and then you have to watch the rev counter carefully. “That was the issue they had with spinning cranks, because it really only made boost around 7,000rpm, with an 8,500rpm redline, so you were very quickly into the red. And as long as it made spark, it would run until the valves floated right into the pistons, because it was just pumping more and more air. There was nothing to stop it going until it crushed itself!”

Ultimately, the TC was a failed concept. Too crude, it would be upstaged by slicker, more civilized factory efforts from the Big Four. Yet even those would fail to hold a market. Although turbocharging is common in cars today, no factory turbo motorcycles have been built since the mid-1980s. MC

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